The present invention relates to seals used between metal surfaces and in particular, though not exclusively, to an annular seal for use in flanges, joints and packers located in oil and gas exploration and production equipment.
Typical annular seals used to prevent the passage of fluid between two surfaces are elastomeric o-rings. The material makes them flexible enough to mould into any deformities in the metal surface, while their compressibility aids in providing a large sealing area. However, these seals can go beyond their operational limits when used within well bores during oil and gas exploration and production, due to the extremes of pressure, temperature and the harsh substances which are used. In order to overcome these problems, metal to metal seals have been developed to provide increased seal strength and reduce seal degradation.
These metal to metal seals have found application in flanges, for example. When API 6A or similar flanges are manufactured, the groove has an exact geometry and surface finish. The sealing ring is a solid metal ring, which is compressed against the seal ring grooves to make the metal-to-metal seal. This is typically achieved by tightening the bolts on the flange. As there is no or little flexibility in the seal, side loading can reduce or remove any seal formed between the groove and flange. Furthermore, older flanges, which are subject to corrosion, can leak. As there is no compliance within the solid metal ring, once a leak appears the seal cannot be re-seated without re-tightening the bolts. In sub-seal applications, it is very expensive to monitor each flange and tighten the bolts as part of a maintenance programme.
To overcome this problem, seals incorporating the strength of metals together with the flexible characteristics of elastomers have been developed. EP 1136734, DE 3633335 and DE 3712814 all disclose flange ring seals using metal and elastomeric parts. These seals generally comprise a metal insert in the elastomeric material. While this design provides a seal with improved rigidity, the seal against the flange is made by the elastomer, which has the inherent disadvantage of seal degradation.
In packers, it is known to position an elastomeric sleeve around a tubing, the sleeve being limited by upper and lower retainers. In order to provide an annular seal and/or anchor the tubing in a well bore, one or both of the retainers are moved toward the other. This results in compression of the sleeve so that it deforms radially outwardly to fill the space between the tubing and a bore hole wall or tubular and adhere to the bore hole wall or tubular. Various arrangements have been provided in an attempt to ensure a sufficient portion of the sleeve contacts the borehole or tubular wall to effect a good seal while maintaining the sleeve within the retainers during compression. In addition, the surfaces of the seals have been modified to improve adhesion to the borehole wall. Further, metal to metal seals as described above, have been incorporated.
WO 02/04783 to Moyes discloses a deformable member comprising a generally hollow cylindrical body defining a wall, the wall includes three circumferential lines of weakness in the form of grooves, with two grooves provided in an outer surface of the member wall, and the other groove provided in an inner surface. The member is deformed outwardly to provide a seal, by folding about the lines of weakness. The member is typically made of a tough malleable material such as carbon steel. A disadvantage of this seal is that by introducing lines of weakness to help the seal deform, the whole structure is weakened. As a result thick sections are required to prevent the element from collapsing under pressure differentials.
U.S. Pat. No. 5,988,276 to Oneal discloses a compact retrievable well packer which also utilises deformable cylindrical members to form the annular seal and also to lock the well packer in situ. As with Moyes, thick sections are required to prevent the sealing element from collapsing under pressure differentials.
U.S. Pat. No. 5,961,123 to Ingram et al discloses a seal arrangement which is designed to prevent the seal from extruding uphole or downhole when subjected to extremes of differential pressure. In this arrangement the seal material is bounded at either end by metal back-up rings, these rings may be attached to the seal or, as disclosed in U.S. Pat. No. 5,961,123, be attached to one of the retainers. This seal has the typical disadvantages of elastomeric based seals which can be degraded easily by heat and chemicals used downhole.
U.S. Pat. No. 5,775,429 to Arizmendi et al discloses a seal including a deformable sheath having a body and first and second ends for defining an interior volume proximate to a tool surface. The tool surface is the tubing. A material located within the interior volume is deformable, when the sheath second end is moved toward the sheath first end. The sheath is typically a relatively thin walled tubular member formed from materials like stainless steel or titanium. The filler material within the interior volume plastically deforms to advantageously allow the seal to be used oval shaped bore holes. Unfortunately this seal does not perform well in practice. As the filler material is restrained by the tubing, volumetric changes in the seal distort the seal and reduce the effectiveness of contact with the bore hole wall or tubular. These volumetric changes occur as the sheath ends are brought together before the seal meets the bore hole wall or tubular and is pressurised.
It is an object of at least one embodiment of the present invention to provide a sealing element which is flexible, like an elastomer seal, but is fully metal to metal.
It is a further object of at least one embodiment of the present invention to provide a sealing element having a fully enclosed filler material to provide improved sealing properties of the element.
It is a yet further object of at least one embodiment of the present invention to provide a sealing element which deforms in a controlled manner on a cantilever principle.